1. Field of the Invention
The invention relates to a mobile telephone and, more specifically, to a technique for establishing and maintaining a call by automatic redialing in case of a failure in call establishment or a call due to a communications channel disorder such as congestion or weak wave (i.e., received wave level shortage).
2. Description of the Prior Art
There are a variety of telephone sets that can automatically dial one of telephone numbers previously stored in memory by the user. Some of them redial the last called phone number in response to a predetermined input. Some others dial a phone number either specified by a predetermined operation by the user or associated with an abbreviated number input by the user. Also, U.S. Pat. No. 5,742,666 discloses an emergency mobile telephone. In this system, automatic dialing of an emergency telephone number is initiated by the user pressing a dedicated push button on the cellular telephone handset, or alternatively, upon the occurrence of an accident which is detected by the cellular telephone.
However, there has not been such a cellular telephone as utilizes the automatic redialing function to cope a failure in call establishment such as a busy state of the called party, a congestion or weak wave and to cope with a failure in connection during a call due to congestion or weak wave.
Therefore, it is an object of the invention to provide a technique for establishing and maintaining a call by automatic redialing in case of a failure in call establishment or a call due to a busy state of the called party or a communications channel disorder such as congestion or weak wave.
The problems of a failure in call establishment or a call due to a busy state of the called party or a communications channel disorder are overcome in accordance with an aspect of the invention. In response to a request for a call origination for a destination telephone number, a call is originated for the destination telephone number. In case of a failure in the call origination, a call termination process is executed and then the call origination is retried.
In a preferred embodiment, the retrying of the call origination is put off while a received wave level is less than a predetermined level.
If a count of said call origination reaches a predetermined count value, then the retrying is stopped.
If the failure is due to a busy state of a called telephone terminal identified by the destination telephone number, a call is originated for a substitution telephone number as the retrying operation. The substitution telephone number is one of telephone numbers associated with a called party identified by the destination telephone number in a telephone directory table. The substitution telephone number is different from the last called telephone number.
If a count of said call origination reaches a predetermined count value, then the retrying is stopped.
Once a call is established after the call origination, in response to a detection of disconnection of the call caused not by a user but by a channel disorder, a call termination process executed. A call is originated for the same telephone number as a destination telephone number of the disconnected call.
According to another aspect of the invention, a cellular telephone apparatus capable of establishing and maintaining a call even in case of a failure in call establishment or a call due to a busy state of a called party or a communications channel disorder is provided in the same way as described above.
According to further aspect of the invention, there is provided a portable system including a cellular telephone means capable of establishing and maintaining a call even in case of a failure in call establishment or a call due to a busy state of a called party or a communications channel disorder. The cellular telephone means has the same features as the cellular telephone apparatus described above. The portable system may include a GPS (global positioning system) or navigation system. The portable system may be a laptop computer.